Issue Summary

This is reproducible on Data Center: (yes) 

Steps to Reproduce

1. Create 10 or more internal users with similar name like( user 1, user 2, user 3, user 4, user 5, .... user 10)
2. Create a new ticket and in comment mention user name, we will find only 5 users.
3. In an organisation it may happen that there are many users with same name, it would be helpful if we can keep it configurable.
4. Whenever we mention a user a rest call is invoked, we find maxResults as 5 thus it is configured in javascript somewhere.

   http://HOST:PORT/rest/internal/2/user/mention/search?issueKey=[issueKey]&projectKey=[projectKey]&maxResults=5&query=chandra+she 

1. This appears hardcoded in javascript.

# script
jira-components/jira-webapp/src/main/webapp/includes/jira/mention/Mention.js

# maxResults set to 5 in script.
const SEARCH_MAX_RESULTS = 5;

Expected Results

maxResults should be configurable so that there are more users in list.

Actual Results

Only 5 users are listed at a time.

Workaround

One has to type complete name of that user.